Question

我正在使用我的iPhone应用中的NSUserDefaults，出于某种原因，应用程序需要启动/恢复两次才能使设置中的更改生效。相关代码：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    ...

    DLog(@"Registered default user defaults values.");
    NSDictionary *dictionary = [NSDictionary dictionaryWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"DefaultUserDefaults" ofType:@"plist"]];
    [[NSUserDefaults standardUserDefaults] registerDefaults:dictionary];

    ...

}

- (void)applicationDidBecomeActive:(UIApplication *)application {
    DLog(@"rescheduling notifications...");
    [self rescheduleAllNotifications];
}

- (void)rescheduleAllNotifications {
    //
    // Wipe the slate clean by cancelling all local notifications
    //
    [[UIApplication sharedApplication] cancelAllLocalNotifications];

    //
    // Only reschedule notifications if the user prefers to have them scheduled
    //
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    if ([defaults boolForKey:@"notifications_enabled_preference"]) {
        DLog(@"Notifications enabled. processing now...");

        ...

所以这是我的调试器输出（从notifications_enabled_preference开始设置为YES）：

[Session started at 2011-01-31 14:25:58 -0600.]
AppDelegate application:didFinishLaunchingWithOptions:] Registered default user defaults values.
AppDelegate applicationDidBecomeActive:] rescheduling notifications...
AppDelegate rescheduleAllNotifications] Notifications enabled. processing now...

-> Switch to Settings and turn notifications_enabled_preference to NO, then re-launch the app

AppDelegate applicationDidBecomeActive:] rescheduling notifications...
AppDelegate rescheduleAllNotifications] Notifications enabled. processing now...


-> Click home screen button, then re-launch the app **again**

AppDelegate applicationDidBecomeActive:] rescheduling notifications...
AppDelegate rescheduleAllNotifications] Notifications disabled. Skipping notification processing.

为什么启动应用两次才能使更改后的设置生效？

Answer 1

NSUserDefaults会定期与磁盘同步（通常每隔30秒左右）。此同步过程允许它写出对磁盘的更改，但也可以获取在磁盘上所做的更改。尝试在[[NSUserDefaults standardUserDefaults] synchronize]方法的最顶部调用-applicationDidBecomeActive:。

为什么iOS NSDefaults需要两次启动才能生效？

1 个答案: